The nature of calcium regulation in bone cells will be studied with specific emphasis on the interrelationships of calcium, cyclic nucleotides and calmodulin. Separation and characterization of osteoclastic and osteoblastic cells obtained by sequential collagenase digestions of newborn rat calvaria will be conducted by cytofluorographic studies. Osteoclastic cells will be characterized and separated into subpopulations on the basis of specific staining for acid phosphatase and Beta glucuronidase activity and osteoblastic cells on the basis of alkaline phosphatase and glycogen activity levels. Using these subpopulations of specific bone cell types, the effects of the calcium ionophore, A23187, and the calcium antagonist, D600, on cyclic GMP levels will be studied by radioimmunoassay. The effects of cyclic GMP on calcium transport will be investigated using 45Ca. These studies should give insight into the interrelationships of this nucleotide and calcium. The role of calmodulin in regulation adenylate/guanylate cyclase and calcium transport will be studied directly using enriched membrane fractions of osteoclastic and osteoblastic cells. Since calmodulin has been shown to bind calcium with high affinity and specificity, the information obtained in these studies should further elucidate the nature of calcium regulation in bone cells. These studies should provide a clearer understanding of the biochemical processes involved in the control of bone metabolism.